This interface defines a contract between the application and GemFire that
allows GemFire to determine whether an application object contains a delta,
allows GemFire to extract the delta from an application object, and generate
a new application object by applying a delta to an existing application
object.

An SystemConnectException is thrown when a
GemFire application tries to connect to an
existing distributed system and is unable to contact all members of
the distributed system to announce its presence.

This package contains classes that are used throughout GemFire,
providing enhanced serialization performance using the DataSerializable feature and the ability to
profile your GemFire application using a handy Statistics infrastructure.

The ability to monitor and analyze the behavior and performance of
an application can ease the job of optimization. To aid in this
analysis, GemFire provides the ability to register and capture
application statistics. An application statistic is simply a number
that the application is free to modify and that is monitored by
the GemFire's statistics collector.
The statistics may be
monitored at runtime using the Admin API or GemFire JMX Agent.

Each application statistic is described by a
StatisticDescriptor instance.
Logical groupings of application statistics are described by a
StatisticsType instance that contains the name
and description of each statistic. Each instance of an type
is represented by an instance of
Statistics.
The descriptors,
types, and
instances are created using an
instance of the StatisticsFactory interface.
Each statistics instance
(there may be multiple instances of a statistics type) can be identified
by a text id
and/or a numeric id.
The name, description, etc. of the statistic and its type
are available in the Admin API or GemFire JMX Agent.

An application can get, set, and increment the value of a statistic
using methods of the Statistics interface. If statistics
sampling has been enabled
a thread in the application VM periodically
reads the values of application statistics allowing them to be viewed
by the Admin API and GemFire JMX Agent. Statistics may also be archived
to a file, the name
and location of which may be configured when creating a DistributedSystem.

In addition to application statistics, GemFire maintains statistics
about the distributed system, the distributed cache,
and the physical machine on which it runs. These statistics can be
monitored, viewed, and archived just like application statistics.